Jvet quadtree plus binary tree (qtbt) structure with multiple asymmetrical partitioning

ABSTRACT

A method of partitioning in video coding for JVET, comprising representing a JVET coding tree unit as a root node in a quadtree plus binary tree (QTBT) structure that can have quadtree or binary partitioning of the root node and quadtree or binary trees branching from each of the leaf nodes. The partitioning at any depth can use asymmetric binary partitioning to split a node represented by a leaf node into two child nodes of unequal size, representing the two child nodes as leaf nodes in a binary tree branching from the parent leaf node and coding the child nodes represented by final leaf nodes of the binary tree with JVET, wherein further partitioning of child nodes split from leaf nodes via asymmetric binary partitioning is allowed recursively along the same branch in any order with symmetric partitioning.

CLAIM OF PRIORITY

This Application claims priority under 35 U.S.C. §119(e) from earlierfiled U. S. Provisional Application Serial No. 62/341,325, filed May 25,2016, and from earlier filed U.S. Provisional Application Serial No.62/408,696, filed Oct. 14, 2016, both of which are hereby incorporatedby reference.

TECHNICAL FIELD

The present disclosure relates to the field of video coding,particularly a block partitioning scheme for JVET that allows quadtreepartitioning, symmetric binary partitioning, and asymmetric binarypartitioning in a quadtree plus binary tree (QTBT) structure.

BACKGROUND

The technical improvements in evolving video coding standards illustratethe trend of increasing coding efficiency to enable higher bit-rates,higher resolutions, and better video quality. The Joint VideoExploration Team is developing a new video coding scheme referred to asJVET. Similar to other video coding schemes like HEVC (High EfficiencyVideo Coding), JVET is a block-based hybrid spatial and temporalpredictive coding scheme. However, relative to HEVC, JVET includes manymodifications to bitstream structure, syntax, constraints, and mappingfor the generation of decoded pictures. JVET has been implemented inJoint Exploration Model (JEM) encoders and decoders.

SUMMARY

The present disclosure provides a method of partitioning a video codingblock for JVET, the method comprising receiving a bitstream indicatinghow a coding tree unit was partitioned into coding units according to apartitioning structure that allows root nodes to be split with at leastone of quadtree partitioning, symmetric binary partitioning, and/orasymmetric binary partitioning, parsing said bitstream to determine ifat least one of asymmetric partitioning and/or symmetric partitioningsplits a parent node into child nodes, wherein symmetric partitioningsplits a parent node in to child nodes of equal size, and asymmetricpartitioning splits a parent node in to child nodes of unequal size, andidentifying each of the child nodes within each respective parent unit,wherein a node can be recursively partitioned in to smaller nodes. Thepartitioning structure allows both asymmetric partitioning and symmetricpartitioning to occur in either order during recursive partitioning of aparent node. The partitioning structure also allows further partitioningof child nodes that are produced from asymmetric partitioning of atleast one parent node. The method also includes decoding the identifiedcoding units using JVET.

The present disclosure also provides an apparatus for coding video datacomprising one or more processors configured to perform the techniquesdisclosed herein.

The present disclosure also provides a method of partitioning a videocoding block for JVET, the method comprising representing a JVET codingtree unit as a root node in a quadtree plus binary tree (QTBT) structurethat can have a quadtree branching from the root node and binary treesbranching from each of the quadtree’s leaf nodes, splitting a squareblock represented by a quadtree node with quadtree partitioning intofour square blocks of equal size and representing them as quadtree nodesthat can represent final coding units or child nodes that can be splitagain with quadtree partitioning, symmetric binary partitioning, orasymmetric binary partitioning, with symmetric binary partitioning intotwo blocks of equal size and representing them in a binary treebranching from the quadtree node as child nodes that can represent finalcoding units or be recursively split again with symmetric binarypartitioning, or with asymmetric binary partitioning into two blocks ofunequal size and representing them in a binary tree branching from thequadtree node as leaf nodes that represents final coding units, andcoding the coding units represented by leaf nodes of the QTBT structurewith JVET.

The present disclosure also provides a method of decoding a JVETbitstream, the method comprising receiving a bitstream indicating how acoding tree unit was partitioned into coding units according to aquadtree plus binary tree (QTBT) structure that allows quadtree nodes tobe split with quadtree partitioning, symmetric binary partitioning, orasymmetric binary partitioning, identifying coding units represented byleaf nodes of the QTBT structure, wherein asymmetric binary partitioningand symmetric partition is allowed in any order along a branch in theQTBT structure, and decoding the identified coding units using JVET.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the present invention are explained with the help ofthe attached drawings in which:

FIG. 1 depicts division of a frame into a plurality of Coding Tree Units(CTUs).

FIG. 2 depicts an exemplary partitioning of a CTU into Coding Units(CUs) using quadtree partitioning and symmetric binary partitioning.

FIG. 3 depicts a quadtree plus binary tree (QTBT) representation of FIG.2 ′s partitioning.

FIG. 4A depicts four possible types of asymmetric binary partitioning ofa CU into two smaller CUs.

FIG. 4B depicts an exemplary partitioning of a CTU into Coding Units(CUs) including use of the partitioning depicted in FIG. 4A.

FIG. 4C depicts a quadtree plus binary tree (QTBT) representation ofFIG. 4B’s partitioning.

FIG. 5A depicts an exemplary partitioning of a CTU using quadtreepartitioning to produce four equal square nodes.

FIG. 5B illustrates binary partitioning to divide a parent node into twochild nodes of the same size in a symmetric manner.

FIGS. 5C and 5D depict asymmetric partitioning of a parent node in totwo child nodes of unequal sizes in an asymmetric manner.

FIG. 5E illustrates embodiments for additional constraints placed on theQTBT partitioning, where each of Types 1-4 provide variations in thevertical and/or horizontal partition.

FIG. 6A illustrates an example of a proposed QTBT that includespartitioning using asymmetric partitioning according to the disclosedtechniques

FIG. 6B depicts a QTBT representation of FIG. 6A’s partitioning.

FIG. 6C illustrates an example syntax for partitioning that includesboth square nodes (SN) and restricted nodes (RN).

FIG. 7 depicts a simplified block diagram for CU coding in a JVETencoder.

FIG. 8 depicts 67 possible intra prediction modes for luma components inJVET.

FIG. 9 depicts a simplified block diagram for CU coding in a JVETdecoder.

FIG. 10 depicts an embodiment of a method of CU coding in a JVETdecoder.

FIG. 11 depicts an embodiment of a computer system adapted and/orconfigured to process a method of CU coding.

FIG. 12 is a flow diagram that illustrates a method for performing thedisclosed techniques.

FIG. 13 is a high level view of a source device and destination devicethat may incorporate features of the systems and devices describedherein.

DETAILED DESCRIPTION

Disclosed herein are techniques for a flexible coding block structurewhich allows asymmetrical partitioning as part of a quadtree plus binarytree (QTBT) structure. As disclosed herein, one or more embodiments forpartitioning may be less restrictive and require less encoding/decodingcomplexity than that of prior proposals for coding. Thus, the disclosedtechniques may provide for more efficient video coding.

FIG. 1 depicts division of a frame into a plurality of Coding Tree Units(CTUs) 100. A frame can be an image in a video sequence, which mayinclude a plurality of frames. A frame can include a matrix, or set ofmatrices, with pixel values representing intensity measures in theimage. The pixel values can be defined to represent color and brightnessin full color video coding, where pixels are divided into threechannels. For example, in a YCbCr color space pixels can have a lumavalue, Y, that represents gray level intensity in the image, and twochrominance values, Cb and Cr, that represent the extent to which colordiffers from gray to blue and red. In other embodiments, pixel valuescan be represented with values in different color spaces or models. Theresolution of the video can determine the number of pixels in a frame. Ahigher resolution can mean more pixels and a better definition of theimage, but can also lead to higher bandwidth, storage, and transmissionrequirements.

Frames of a video sequence, or more specifically the coding tree unitswithin each frame, can be encoded and decoded using JVET. JVET is avideo coding scheme being developed by the Joint Video Exploration Team.Versions of JVET have been implemented in JEM (Joint Exploration Model)encoders and decoders. Similar to other video coding schemes like HEVC(High Efficiency Video Coding), JVET is a block-based hybrid spatial andtemporal predictive coding scheme. During coding with JVET, a frame isfirst divided into square blocks called CTUs 100, as shown in FIG. 1 .For example, CTUs 100 can be squares of 128×128 pixels.

FIG. 2 depicts an exemplary partitioning of a CTU 100 into CUs 102,which are the basic units of prediction in coding. The coding unit maybe represented by a region (in terms of pixels/luma-samples) and is afinal node of the partitioned CTU.

Generally, the decision whether to code a picture area usinginter-picture (temporal) or intra-picture (spatial) prediction may bemade at the coding unit level, so a slice is divided into a sequence ofCTUs during the encoding process. Each CTU 100 in a frame can bepartitioned into one or more CUs (Coding Units) 102. CUs 102 can be usedfor prediction and transform as described below. Unlike HEVC, in one ormore embodiments in JVET the CUs 102 can be rectangular or square.Further, in one or more embodiments, JVET CUs can be coded withoutprediction units, or transform units, which may remove the separation ofCU, PU, and TU concepts and also support flexibility for additional CUpartition shapes to better match the local characteristics of videodata. For example, a coding unit in JVET may include prediction unit andtransform unit coding information as well, without requiringpartitioning specifically into separate prediction units and transformunits. Additionally, as described in more detail below, QTBT may allow amore flexible binary split, e.g., QTBT can support 16NxN. In HEVC, onthe other hand, non-square blocks can only be achieved by a PU split andthen only 4 types of non-squares shapes (2NxN, Nx2N, 0.5Nx1.5N, and1.5Nx0.5N) are allowed.

In one or more embodiments, the encoder includes a process to try aplurality of coding modes that do not require further partitioning forprediction and transform, which can reducing coding costs, complexity,and time. In some cases, the partitioning of the CUs 102 may still bereferred to as a partitioning in to prediction units or transform units.The CUs 102 can be as large as their root CTUs 100, or be smallersubdivisions of a root CTU 100 as small as 4×4 units.

In JVET, a CTU 100 can be partitioned into CUs 102 according to aquadtree plus binary tree (QTBT) scheme in which the CTU 100 can besplit into square units according to a quadtree or binary partitioning,and those square units can then be split horizontally and/or verticallyaccording to quadtree or binary trees. For example, child nodes of abinary split may be further split using binary partitioning. Thus,JVET’s QTBT coding scheme may be more flexible than HEVC’s quadtreestructure (QT) because in addition to QT partitioning from a parent nodein to equal sized children nodes, QTBT enables binary partitioning (BP)from a parent node into children nodes horizontally or vertically. TheQTBT structure introduced, therefore, represents a tree in which aparent node can split using quadtree into four child nodes, or by usingother partitioning methods as described in more detail below. Each ofthe child nodes may become a parent node for another split intoadditional child nodes. Though, in one or more embodiments, once abinary split occurs, further quadtree partitioning may not be allowed.

In some embodiments JVET can limit binary partitioning in the binarytree portion of a QTBT to symmetric partitioning, in which parent nodescan be divided in half either vertically or horizontally along amidline. By way of a non-limiting example, FIG. 2 shows a CTU 100partitioned into CUs 102, with solid lines indicating quadtree splittingand dashed lines indicating symmetric binary tree splitting. Asillustrated, the binary splitting allows symmetric horizontal splittingand vertical splitting to define the structure of the CTU and itssubdivision into CUs.

It is noted that the term coding block is generally used to define aregion covering a particular component (e.g. luma), and may differ inspatial location when considering chroma subsampling such as 4:2:0. Ablock is also used to describe the shape of CTUs and CUs, but the termsshould be clear from the context. For example, as described in moredetail below, a CU sometimes includes coding blocks (CBs) of differentcolour components, e.g. one CU contains one luma CB and two chroma CBsin the case of P and B slices of the 4:2:0 chroma format and sometimesconsists of a CB of a single component, e.g., one CU contains only oneluma CB or just two chroma CBs in the case of I slices. In one or moreembodiments, the CTU includes a luma coding tree block and correspondingchroma coding tree blocks and syntax elements, which can be partitionedin to smaller blocks using a tree structure and quadtree-plus signaling,where the tree structure syntax of the CTU specifies the size andpositions of its luma and crhoma coding blocks.

FIG. 3 shows a QTBT representation of FIG. 2 ′s partitioning using atree structure. The tree may be used to represent a finite set of nodeswith a unique root node. In a tree structure, samples may be processedin units of coding tree blocks. Each coding tree block may be assigned apartition, the partition signaling to identify the block sizes for intraor inter prediction and for transform coding. The partitioning may be arecursive quadtree partitioning or, as shown herein, a quadtree pluspartitioning method that contemplates much more flexibility to thecoding tree structure. The division of a component into coding treeblocks is a partitioning.

A CTU, such as CTU 100, is a type of coding tree block that representsan entire N×N square of picture samples for some value of N, where thefirst root node at the highest hierarchy of the tree structure (depth 0)is associated with the entire coding tree block or CTU. A root node withdepth 0 may be partitioned in to two or more child nodes, also referredto herein as leaf nodes. For example, a quadtree node could be furtherpartitioned by a binary tree, where the quadtree leaf node is also theroot node for the binary tree having binary tree depth as 0. Further,while each of the nodes split from a prior node may be child nodes orleaf nodes, such nodes are also parent nodes when the child node isfurther partitioned into additional child nodes. Thus, a node may existas both a parent node and a child node, and a root node may also bereferred to herein as a parent node.

The tree structure is split among multiple branches and a single branchmay include several nodes, until a final leaf along each branch isreached, which is referred to as the coding unit. Thus, a final leafnode in a recursively split branch is also referred to herein as aterminating leaf node or final child node. Collectively these final leafnodes represent the final set of coding units (CUs) that make up theCTU, and will not be further partitioned. Thus, where a leaf noderepresents a coding unit the terms may be used interchangeably, and afinal leaf node should be understood to correspond to the final codingunit along the respective branch.

The root node in FIG. 3 is shown split using quadtree partitioningresulting in four equal children. Each of the four nodes branching fromthe root node are therefore child nodes, As shown in FIG. 3 , thesquares represented by the quadtree leaf nodes can then be dividedsymmetrically zero or more times using binary trees, with the quadtreeleaf nodes being child nodes but also parent nodes of the binary trees,where a root node may refer to parent nodes at various depths of thetree structure. The parent node of a binary split represents a parentblock that may be further partitioned into two child nodes or blocks. Ateach level of the binary tree portion, a square node can be dividedsymmetrically, either vertically or horizontally. A flag set to “0”indicates that the square node is symmetrically split horizontally,while a flag set to “1” indicates that the square node is symmetricallysplit vertically.

In one or more embodiments, JVET can allow either symmetric binarypartitioning or asymmetric binary partitioning in a binary tree portionof a QTBT. In one or more embodiments, symmetric or asymmetricpartitioning may occur at any depth in the tree structure. Asymmetricalmotion partitioning (AMP) was allowed in a different context in HEVCwhen partitioning prediction units (PUs). However, for partitioning CUs102 in JVET according to a QTBT structure, asymmetric binarypartitioning can lead to improved partitioning relative to symmetricbinary partitioning when correlated areas of a CU 102 are not positionedon either side of a midline running through the center of the CU 102. Byway of a non-limiting example, when a CU 102 depicts one objectproximate to the CU’s center and another object at the side of the CU102, the CU 102 can be asymmetrically partitioned to put each object inseparate smaller CUs 102 of different sizes.

FIG. 4A depicts four possible types of asymmetric binary partitioning inwhich a CU 102 is split into two smaller CU 102 along a line runningacross the length or height of the CU 102, such that one of the smallerCUs 102 is 25% of the size of the parent CU 102 and the other is 75% ofthe size of the parent CU 102. The four types of asymmetric binarypartitioning shown in FIG. 4A allow a CU 102 to be split along a line(a) 25% of the way from the left side of the CU 102, (b) 25% of the wayfrom the right side of the CU 102, (c) 25% of the way from the top ofthe CU 102, or (d) 25% of the way from the bottom of the CU 102. Inalternate embodiments an asymmetric partitioning line at which a CU 102is split can be positioned at any other position such the CU 102 is notdivided symmetrically in half. For example, the split may be at 30% and70%, or 20% and 80%. However, limitations on partitioning based on theparent coding unit size and/or prior partitioning are described in moredetail below.

FIG. 4B depicts a non-limiting example of a CTU 100 partitioned into CUs102 using a scheme that allows both symmetric binary partitioning andasymmetric binary partitioning in the binary tree portion of a QTBT. InFIG. 4B, dashed lines show asymmetric binary partitioning lines, inwhich a parent CU 102 was split using one of the partitioning typesshown in FIG. 4A.

FIG. 4C shows a QTBT representation of FIG. 4B’s partitioning. In FIG.4C, two solid lines extending from a node indicates symmetricpartitioning in the binary tree portion of a QTBT, while two dashedlines extending from a node indicates asymmetric partitioning in thebinary tree portion.

Syntax can be coded in the bitstream that indicates how a CTU 100 waspartitioned into CUs 102. A bitstream may comprise a sequence of bits,in the form of a network abstraction layer (NAL) unit stream or a bytestream that forms the representation of coded pictures and associateddata forming one or more coded video sequences. A syntax may refer to anelement of data represented in the bitstream, also referred to as asyntax element. Each syntax structure including zero or more syntaxelements present together in the bitstream may be included in the NALunit, and they may be presented in a specified order.

As described in more detail below, a syntax element may be a flag thatis a variable or single-bit syntax element that can take one of twopossible values: 0 and 1, or the syntax element may have multipledescriptors and or values available. A syntax may be a statement orelement with an associated descriptor. The syntax element may be anexpression used to specify conditions for the existence, type, andquantity for the syntax. When a syntax element appears, it may specifywhich syntax element to parse from the bitstream. A bitstream pointermay be advanced to the next position beyond the syntax element in thebitstream parsing process.

By way of a non-limiting example, syntax can be coded in the bitstreamthat indicates which nodes were split with quadtree partitioning, whichwere split with symmetric binary partitioning, and which were split withasymmetric binary partitioning. Similarly, syntax can be coded in thebitstream for nodes split with asymmetric binary partitioning thatindicates which type of asymmetric binary partitioning was used, such asone of the four types shown in FIG. 4A. Thus, the partitioning andorganization of a tree structure may be expressed by a series of flagsor syntax elements. Further, a syntax element may be signaled toindicate which splitting type (i.e., horizontal or vertical) is used,where an example flag with a value 0 indicates horizontal splitting and1 indicates vertical splitting. In some cases, such as quadtreepartitioning, signaling may not be required since quadtree partitioningis an equal split horizontally and vertically into 4 equal sub-blocks.

The example child nodes and partitioning thereof included hereindemonstrate that a a child node may be split, or partitioned, intosmaller, final coding units. A root node may represent the entire CTU,and is also referred to as a parent node when partitioned into childnodes. Thus, a node may represent both a parent block and a child blockbecause the child nodes become parent nodes if/when they arepartitioned.

While additional embodiments are depicted in this disclosure such asdescribed below with respect to FIG. 6B, FIG. 4C represents a QTBTstructure with a combination of restrictions in place. Parameters can beset to control splitting according to the QTBT, such as the CTU size,the minimum sizes for the quadtree and/or binary tree leaf nodes, themaximum size for the binary tree root node, and the maximum depth forthe binary trees. For example, nodes may be recursively split intosmaller nodes until a minimum coding unit size or a maximum number ofpartitions has occurred. Restrictions may also be in place that limitthe type of partitioning allowed depending on other factors, such as atype of prior partitioning of said parent node. For example, if thechild node is the result of a binary partition, restrictions regardingthe type of further partitioning allowed, if any, may be implicated. Inanother example, if the child node is the result of asymmetricpartitioning, restrictions regarding the type of further partitioningallowed, if any, may be implicated. It should be understood that one ormore of the restrictions depicted may be removed or be defined by asubset combination of those shown.

As depicted in FIG. 4C, in one or more embodiments the use of asymmetricpartitioning can be limited to splitting CUs 102 at the leaf nodes ofthe quadtree portion(s) of a QTBT, where asymmetric partitioning is notallowed except at the leaf node of a quadtree. In one or moreembodiments, CUs 102 at child nodes that were split from a parent nodeusing quadtree partitioning in the quadtree portion can be final CUs102, such as CTU 102 a. In one or more embodiments, CUs 102 at childnodes split from the parent node using quadtree partitioning can befurther split using at least one of quadtree partitioning 102 b-e,symmetric binary partitioning 102 f, 102 g, and/or asymmetric binarypartitioning 102 h, 102 i. In one or more embodiments, child nodes inthe binary tree portion(s) that were split using symmetric binarypartitioning can be final CUs 102, such as 102 f. In one or moreembodiments, child nodes in the binary tree portion split usingsymmetric binary partitioning can be further split recursively one ormore times using symmetric binary partitioning only, such as 102 j, 102k. In one or more embodiments, child nodes in the binary tree portionthat were split from a QT leaf node using asymmetric binary partitioningcan be final CUs 102, such as 102 h, 102 i, with no further splittingpermitted.

In embodiments where the use of asymmetric partitioning is limited tosplitting quadtree leaf nodes, search complexity may be reduced and/oroverhead bits limited. In one or more JVET embodiments, a condition maybe imposed that prohibits quadtree partitioning in a binary tree nodesuch that a binary partitioned child node cannot be further partitionedusing quadtree. In either scenario, asymmetric partitioning in a QTBTstructure may be employed using the disclosed techniques to limitoverhead signaling, such that excessive overhead signaling is notrequired. For example, in embodiments in which only quadtree leaf nodesare split with asymmetric partitioning, the use of asymmetricpartitioning can directly indicate the end of a branch of the QT portionwithout other syntax or further signaling. This type of signaling mayalso be referred to as implicit signaling, i.e., to signal what optionis selected by using available information at the decoder to make adecision without an explicit signal or flag. Such technique may be moreefficient when another syntax element inherently includes informationthat the explicit flag would redundantly provide. Similarly, forembodiments in which asymmetrically partitioned nodes cannot be splitfurther, the use of asymmetric partitioning on a node can also directlyindicate that its asymmetrically partitioned child nodes are final CUs102 without other syntax or further signaling.

One or more embodiments disclosed herein include schemes whereasymmetrical partitioning is only allowed at the bottom level of aquadtree portion of a proposed QTBT structure, allowing no furthersplits for asymmetrical partitioned nodes. Such limitations, e.g., nofurther partitioning allowed to a child node if its parent wasasymmetrical partitioned, may be imposed based on encoder/decodercomplexity. Further, as described in more detail below, for thedimensions of a child block that is a product of asymmetric partitioningand is not a square, further asymmetric splits that create non-integerratios with respect to the other child nodes and the root parent nodemay require additional coding complexity to design a transform processfor the non-integer size. Odd size transform is not supported.

If a node uses quadtree partitioning, therefore, the node may havechildren and the children can use quadtree partitioning, binarypartitioning, and/or asymmetric partitioning. But, in embodiments whereasymmetrical partitioning is only allowed at the bottom level, if a nodeuses asymmetric partitioning then no further splits are allowed for thatnode. Further, in embodiments, if a node uses binary partitioning, thenode may have children but its children nodes can only use binarypartitioning. FIGS. 4B and 4C illustrate an example of a QTBT withasymmetric partitioning.

In alternate embodiments, such as when limiting search complexity and/orlimiting the number of overhead bits is less of a concern, asymmetricpartitioning can be used to split nodes generated with quadtreepartitioning, symmetric binary partitioning, and/or asymmetric binarypartitioning. In some instances, a flexible approach to partitioning maybe too flexible and require highly complex encoder operations, or theymay be too restrictive and result in suboptimal coding performance.

FIGS. 5A-5E provide examples of flexible partitioning in QTBT in amodular manner, and achieving flexibility while maintaining lowerencoder complexity. As described, multiple partitioning methods may besupported, such as quadtree partitioning, binary partitioning, andasymmetric partitioning, and one or more split types may be supported,such as horizontal or vertical splits. In one or more embodiments, thepartitioning methods may occur in any order without limits on the typeof partitioning operations that occur recursively within a CTU (or,visualized using the coding tree, having no limits on the partitioningshown in series, or recursively, along a branch stemming from a QTBTroot node). The syntax representing the tree structure and theprocessing order of the generated CUs may specify order where it mattersor may signal an indicator when a specific processing order to generatethe tree by the decoder is not needed.

As described above, the partitioning employed may be subject to certainrestrictions. For example, a node may be recursively partitioned untilits level or level depth reaches a permissible maximum level or leveldepth. The splitting process for the node may be recursively indicated,and syntax elements for the last coding unit that is not furtherpartitioned, or a final leaf node, in the level may be defined.Recursive splitting refers to the successive partitioning that occurswithin a single node. When a child node is split it becomes a parentnode having child nodes, and each successive child node that resultsfrom successive partitioning is a result of recursive partitioning.

FIG. 5A illustrates quadtree partitioning to divide a parent node intofour child nodes of the same size in square shape. The child nodes ofsuch quadtree partitioning are square nodes (SN).

FIG. 5B illustrates binary partitioning to divide a parent node into twochild nodes of the same size in a symmetric manner. Child nodes ofbinary partitioning are called binary nodes (BN).

FIG. 5C and FIG. 5D depict non-limiting examples of asymmetricpartitioning that support modular partitioning. In such examples, theasymmetric partitioning divides a parent node into two child nodes ofunequal sizes in an asymmetric manner (one is larger than another).

As disclosed herein, flexible coding structures that allow asymmetricalpartitioning as part of the QTBT structure may be modified. Techniquesdisclosed and further described below include an example of partitioningusing quadtree, then partitioning the child units resulting from thequadtree partition using asymmetric partitioning based on a 3:1 ratio.The larger child unit resulting from the asymmetric partitioning may befurther partitioned using a 2:1 asymmetrical partitioning. Otherembodiments are disclosed below.

FIGS. 5C and 5D depict asymmetric partitioning of a parent node in totwo child nodes of unequal sizes in an asymmetric manner. In FIG. 5C,the parent node may be a square node that results from quadtreepartitioning of a root node, for example, where further partitioningresults in child node B being three times as large as the child node Afor a ratio of 3:1. Each of Types 1, 2, 3 and 4 depicted in FIG. 5C arepartitioned differently in horizontal or vertical directions but withthe same 3:1 ratio. In embodiments, the larger child node from theasymmetric partitioning is a restricted node and the smaller child nodeis a binary node, such that in FIG. 5C child node A denotes a binarynode (BN) and child node B denotes a restricted node (RN), where thesize of child node B is larger than child node A.

FIG. 5D depicts asymmetric partitioning in which a parent restrictednode, such as child node B from FIG. 5C, is asymmetrically partitionedinto two child nodes of unequal size in an asymmetric manner, where oneis twice as large as the other for a size ratio of two (2:1). Therestriction on the restricted node may be on the ratio of asymmetricalpartitioning allowed, which is described in more detail below. Childnodes resulting from this type of asymmetric partitioning may beconsidered binary nodes. Thus, child node A denotes a smaller binarynode and child node B denotes the larger binary node, where the parentnode is the restricted node. And as with FIG. 5C, each of Types 1, 2, 3and 4 depicted in FIG. 5C are partitioned differently in horizontal orvertical directions.

As illustrated by the example embodiments, partitioning may result in arestricted node that is restricted in certain ways. For example, anexample of partitioning for a proposed QTBT may require that if a nodeuses quadtree partitioning, the child nodes may be square nodes that canbe partitioned using quadtree partitioning, binary partitioning, or the3:1 asymmetric partitioning shown in FIG. 5C. The 3:1 partitioning shownin FIG. 5C of at least one of the square nodes partitioned from theparent node may be partitioned in to binary node A, the smaller childnode, and a restricted node B, the larger child node. In an examplewhere a restricted node results from 3:1 asymmetric partitioning, thechild binary node A can further use binary partitioning or the 3:1asymmetric partitioning shown in FIG. 5C, while the child restrictednode B can only use the 2:1 asymmetric partitioning shown in FIG. 5D. Inanother example of a restriction in one or more embodiments for thedisclosed QTBT structure, if a node uses binary partitioning or the 2:1asymmetric partitioning shown in FIG. 5D, the child nodes are binarynodes and each binary node can use binary partitioning and/or the 3:1asymmetric partitioning in FIG. 5C (but not further partitionedaccording to a 2:1 ratio).

Thus, if restrictions described above are applied in combination, anexample set of rules that may apply for a QTBT structure as follows:

-   1. If a node uses quadtree partitioning (QP), its child nodes are    square nodes (SN) and they can use QP, binary partitioning (BP) or    3:1 asymmetric partitioning (AP).-   2. If a node uses 3:1 asymmetric partitioning, its child nodes are    one binary node (BN) and one restricted node (RN). Its child BN can    use BP or 3:1 asymmetric while its child RN can only use 2:1    asymmetric partitioning.-   3. If a node uses BP or 2:1 asymmetric partitioning, its child nodes    are BN and they can use BP or 3:1 asymmetric.

The 3:1 and 2:1 partitions illustrated by FIGS. 5C and 5D are exampleratios for the disclosed asymmetric partitioning methods, but it shouldbe understood that there may be more than two symmetric partitions, anddifferent size ratios between the child nodes are contemplated. Forexample, the larger child node resulting from the partitioning may befour times as large as the smaller child node (4:1), or any otherasymmetric division that results in child nodes of different sizes(e.g., 7:4, 5:2, 2.5:1). In other words, there may be more than two APmethods and/or size ratios between the child nodes from each of AP,where the size ratios for asymmetric partitioning can be anything otherthan 1.

FIG. 5E illustrates embodiments for additional constraints placed on theQTBT partitioning, where each of Types 1-4 provide variations in thevertical and/or horizontal partition. Additional constraints may bedesirable to reduce overhead. For example, binary nodes that are childnodes of a parent restricted node may be split so the larger binary nodelies next to the complimentary binary nodes of its parent restrictednode, and is partitioned so the smaller binary node has the samedimension as the complimentary binary node of its parent restrictednode. The shaded shapes in FIG. 5E denote the parent restricted node andthe unshaded shapes denote the complimentary BN.

To add a complexity control that supports modular implementation, aparameter called size discrepancy limit (SDL) may be employed to limitsmallest size of BN and RN. This parameter sets a minimum size of childnode based on ratio of its horizontal and vertical dimensions, referredto as size discrepancy (SD), as described in equation 1 below. Forexample, in example embodiments when SDL is set to 4, a BN of size 32×4or a RN of size 12×64 is not allowed. When a SDL parameter is enforced,a max BT depth parameter can be dropped in one or more embodiments.

$\begin{matrix}{\text{SD} = \mspace{6mu}\mspace{6mu}\max{\left( {\text{width},\text{height}} \right)/{\min\left( {\text{width},\text{height}} \right)}}} & \text{­­­(1)}\end{matrix}$

FIG. 6A illustrates an example of a proposed QTBT that includespartitioning using asymmetric partitioning according to the disclosedtechniques with less restrictions than that which is shown in FIG. 4C.For example, asymmetrically partitioned nodes are shown furtherpartitioned using binary or asymmetric partitioning. FIG. 6B depicts thetree structure of the block structure of FIG. 6A.

In FIG. 6B, the longer dashed line shows the asymmetric partitioningaccording to the 3:1 asymmetric partitioning in FIG. 5C and the shorterdashed line shows the 2:1 asymmetric partitioning according to thepartitioning in FIG. 5D. The overhead signaling of this example of theproposed QTBT (which may also include the additional constraints of FIG.5E), is similar to the QTBT syntax in FIGS. 4B and 4C, but with amodification to allow the asymmetric partitioning with the ratiosaccording to that shown in FIGS. 5C and 5D, and/or to allow recursiveasymmetric partitioning within a same branch within the tree, i.e.,along the same branch stemming from the root node, and/or to allow bothasymmetric and symmetric partitioning within the same branch in anyorder. As illustrated by the examples in FIGS. 5C-5D and FIGS. 6A and6B, asymmetric partitioning and binary partitioning may be used togetherseamlessly.

It may be desirable to maintain dimension having integer values. Forexample, if a parent node dimension is 3N, the children should havedimensions of 2N and N. In another example, if a parent node dimensionis 4N, its children can have dimensions of 3N and N or 2N and 2N, aslong as the N multiplier is an integer value. Thus, in one or moreembodiments, the conditions of partitioning may be defined to preventnon-integer child parts of the whole where the smallest coding unit isassigned a value of 1, where the whole is a square parent coding unit.In other words, conditions may be set such that a ratio of child unitsizes that together make up a parent square node will have a ratio equalto: 1(size of the smallest coding unit):(an integer value). Thus, thechild nodes that result from partitioning will have an integer-sizedvalue in a ratio of its size to the smallest child unit having size 1part of the whole of any square parent coding unit in the child node’sancestry.

Using the embodiment in FIG. 6A as an example, the root nodeencompassing the whole square shown in FIG. 6A is quadtree partitionedin to four equal parts, such as 102 a in the lower left quadrant of FIG.6A. In the lower right quadrant of FIG. 6A and referring to FIG. 6B,four additional partitioning operations occur in the square parent noderepresented by this quadtree square node. For purposes of this example,assume the quadtree parent square node is node A, which afterpartitioning includes child nodes 102 p, 102 q, 102 j, 102 r, and 102s.\

Starting with the whole parent square node A, first a 3:1 partitionoccurs resulting in a larger child node B (represented by 102 j+102p+102 q) and smaller child node C (represented by 102 r + 102 s).Smaller child node C is further 3:1 asymmetrically partitioned intochild units D (102 r) and E (102 s). The larger node B is partitionedusing 1:2 asymmetrical partitioning, into larger child unit F (102 j)and smaller child node G (102 p+102 q). Smaller child node G issymmetrically binary partitioned in to H 102 p and I 102 q.

In accordance with the example rules above and if there is a requirementfor an integer ratio, each time a child unit is partitioned, theresulting child units within a parent square node must have a size thathas an integer ratio value relative to the size of the smallest codingunit assigned a value of 1 and relative to the size of the parent squareunit. For example, assume parent square node A has 4 parts and ispartitioned according to a ratio of 3N:1N, child node B (102j+102p+102q) represents 3 parts of square node A (3N) and child node C represents1 part of square node A (1N), respectively, for a ratio of 3:1. Whenchild node B having size 3N is 2:1 partitioned in to F and G, F (102 j)represents 2 parts of square node A (1N) and G (102 p+102 q) represents1 part of square node A (1N), respectively, for a ratio between nodesC:F:G of 1 where child node C represents 1 part of the whole for a totalof 4. Thus, assigning the smallest coding unit in the plurality ofcoding units that make up a parent square node to a value of 1 part ofthe whole, each child node has an integer size representation relativeto the smallest coding unit and relative to the whole. Further, the sumof the assigned ratios for the plurality of coding units adds up to thewhole.

In accordance with the rules, at the point of partitioning child node B(represented by 102j+102p+102 q) could not be binary partitioned, as Bhas size 3N of the whole having size 4N in a ratio of 3:1 with unit C. Abinary partition of B would result in child nodes each having a size 1.5of square node A relative to C’s size of 1. Thus, the non-integer sizechild units relative to the parent square coding unit is disallowedaccording to these rules. Limits on a ratio with non-integers such asthe example 1.5:1.5:1 above acknowledge encoding and decoding processesthat may rely on non-integer ratios, thus avoiding further modificationto support non-integer ratios. Further limits on partitioning may be inplace to meet the needs of encoders in terms of memory and computationalrequirements.

In another example, child unit G includes child units 102 p and 102 qthat result from a binary partitioning of portion G. Assuming portions Cand F make up the rest of parent square node A, each child unit H (102p) and I (102 q) represent the smallest unit, each assigned a size 1 forpurposes of the ratio. Thus the ratio of H:I:C:F = 1:1:2:1, all integervalues which, when summed, equal the 4 parts of the whole square node A.

In order to maintain integer ratios of a child coding block sizesrelative to a root (or parent) node with an NxN dimension, thepartitioning of a node having a size that is an odd value relative toparts of the whole is limited, such that the node may be a restrictednode as described above. On the other hand, binary partitioning of aroot square node would result in two child nodes each having 1 part of 2of the root square node for a ratio of 1:1. If one of those child nodesis further partitioned using 3:1 partitioning, the smallest child unitin the root square node assigned a size of 1N, the ratio of parts is4:3:1 for a total of 8 = 2N. Thus, the root square node can be deemed tohave 8 parts, the larger child node having 3 parts of 8, the smallernode from the 3:1 partitioning having 1 part of 8, and the child noderesulting from the first partition having 4 parts of the 8. Thus, evenwith limitations in place, there are many flexible options for bothasymmetric and symmetric partitioning within a CTU.

In one or more embodiments, non-integer ratios in contrast to theembodiments above is contemplated, however it is acknowledged thatmodifications to the existing HEVC encoder and decoder would be requiredfor the coding units of such varying sizes.

A coding tree unit may be represented and coded as a recursive treestructure, and the tree structure may be expressed by a series of flags.For a binary node, the first syntax to be encoded may be a flagindicating whether there will be further partitioning or not. If thereis further partitioning, a second syntax may be used to indicate whetherto use horizontal or vertical partitioning. Then a third syntax encodedmay be a flag indicating whether symmetric partitioning or asymmetricpartitioning is to be used; i.e., BP or the 3:1 asymmetric partitioningshown in FIG. 5C. If the 3:1 partitioning shown in FIG. 5C is used, afourth syntax may also be used to indicate whether the first child nodeis larger than the second one or not.

FIG. 6C illustrates an example syntax for partitioning that includesboth square nodes (SN) and restricted nodes (RN), where the restrictednodes in this example are represented by shaded shapes. Syntax elementsmay be included in a bitstream, and may be in an ordered sequence. Thesyntax elements may be found in a header of the bitstream, for example.As described in more detail below, decoding processes may occur based onsyntax elements in a bitstream or picture slide header. A syntax elementmay also be referred to as a codeword or flag in a syntax structure. Thesyntax for each syntax element is encoded and signaled in the bitstream.The syntax elements describe how the video signal can be reconstructedat the decoder. For example, for a CTU, the related syntax elementsdescribe the partitioning of the CTU into coding units and therepresentation of the CTU’s partitioning in the tree structure. Thedecoder can parse the syntax structure to identify each of the syntaxelements or flags within the structure to determine how the CTU and eachCU was partitioned. While a codeword or a flag may be a syntax elementhaving a single bit, multiple pieces of information may be defined usingmultiple values for a flag and, if necessary, additional bits may beused to signal additional options.

FIG. 6C provides a visual representation of a syntax structure havingmultiple layers of syntax elements encoded for signaling information onhow the root node was partitioned and encoded. Example flags are usedfor each syntax element, and it should be understood that the namingconvention of such syntax elements and/or flags may vary. As illustratedby this example, a first syntax to be encoded for a root node is a flag,e.g., flag.quadtree_partitioning, which indicates whether quadtreepartitioning (“QP”) is used or not (“No QP split”). As shown in the “QP”direction in FIG. 6C, the quadtree partitioning may result in foursquare child nodes of equal size. Such quadtree partitioned unit may befurther partitioned, though in this example no further partitioning isdepicted by way of example.

If “No QP split” is signaled by the flag.quadtree_partitioning syntaxelement, quadtree partitioning is not used. The flag.partitioning_methodflag may be a second flag that, once determined by a first flag that QPis not used, the second flag indicating which non-QP method will be usedor not. Alternately, the flag.partitioning_method flag may be used toindicate both whether the quadtree partitioning is used or not (e.g.,value 0 for quadtree and any other value for “non-QP”) and also signalthe type of non-quadtree partitioning method used (e.g., value 1-3,1=binary, 2 = AP1, 3 = AP2) is used.

As shown in FIG. 6C, the “Non QP” signaled in the syntax element mayindicate that a non-QP partitioning technique is applied, and the “Nosplit” example indicates that the node is not split by any partitioningmethod.

If there is further partitioning using a non-QP partitioning method, athird syntax may be signaled to indicate whether to partition in ahorizontal or vertical direction. Both examples of a verticalpartitioning direction and a horizontal partitioning direction areprovided in FIG. 6 and the example syntax structure is named by way ofexample as flag.partitioning_direction.

For either of the identified vertical or horizontal partitioningdirections, an additional syntax may be used to identify whichpartitioning method is applied, e.g., AP1, AP2, binary, using a syntaxsuch as flag.partitioning_symmetry or another flag.partitioning_methodtype of syntax. Also for the partitioning method and for either verticalor horizontal partitioning, another syntax to be encoded and signals maybe a flag, e.g., flag.symmetry, indicating whether the non-QP techniquewill use symmetric or asymmetric partitioning (e.g., binary partitioningor the 3:1 or 2:1 partitioning shown in FIGS. 5C or 5D, respectively).For purposes of example, FIG. 6C provides both examples of the 3:1asymmetric partitioning (“AP1”) and binary partitioning in both thevertical and horizontal partitioning directions. As described above,partitioning a parent node of dimension NxN may be limited in on or moreembodiments to a partitioning that produces integer division ratiosbetween the final coding units that make up the parent node. Thus,either3:1 AP1 partitioning or binary partitioning of the root squarenode are enabled, but a 2:1 partitioning is disallowed at this depth inthe tree.

For partitioning signaled as a partition in the vertical or horizontaldirection with asymmetric partitioning, a syntax may further be signaledto indicate which child node is the larger child node and/or which childnode is the smaller child node. The example in FIG. 6C uses the syntaxelement named flag.split_type to indicate which type of split occurs. Asdescribed above with respect to FIGS. 5C and 5D, signaling forpartitioning in the vertical directly may identify either of Type 1(larger child node on the right) or Type 2 (larger child node on theleft) for vertical partitioning. Similarly in the horizontal direction,signaling identifies either of Type 3 (larger child node on the bottom)or Type 4 (larger child node on the top).

In embodiments for which asymmetric partitioning is used, a flag may besignaled that identifies the ratio of the asymmetric split. FIG. 6Cprovides an example where such syntax is referred to as aflag.asymmetric_ratio. In one or more embodiments, the same syntax maybe used to indicate both whether the first child node is larger than thesecond one and the ratio of such split. For example, the flag mayidentify that the partitioning operation was a 3:1 asymmetricpartitioning. In one or more embodiments, the same flag may include theratio as well as the positioning of the larger child node compared tothe smaller child node (e.g., Type 1, Type 2, etc, described above),where an order of the first child and second child may be predetermined.For example, the flag.asymmetric_ratio for a vertical split could have avalue 1 for a 3:1 split and value 2 for a 1:3 split, indicating a sizeratio of the larger node as 3x the size of the smaller node, where thevalue 1 for a 3:1 ratio indicates that the child node to the left is thelarger node and the value 2 for a 1:3 ratio indicates the child node tothe right of the vertical split is larger.

For a 3:1 asymmetric partitioning such as that shown in FIG. 5C, arestriction imposed may be that the resulting larger child node is arestricted node. A syntax element shown as a flag.restricted flag inFIG. 6C may be a syntax included that indicates whether furtherpartitioning is allowed or not. Thus, the flag.restricted syntax elementmay identify which child units are restricted, such as that shown byeach of the shaded child units in FIG. 6C. The restrictions may beimposed by the rules of encoding and decoding, such as if the largerchild node resulting from a 3:1 asymmetric node is disallowed fromfurther partitioning as described above. For example, the smaller childnode resulting from the Type 1 3:1 vertically partitioned node (shown asthe furthest left branch in FIG. 6C) may be further partitioned usingthe 2:1 partitioning shown in FIG. 5D, shown as “AP2” in FIG. 6C. Andthe larger node resulting from the Type 1 3:1 vertically partitionednode is restricted from further partitioning and is represented as afinal coding unit in the bitstream (shown as a shaded shape in the finalrow in FIG. 6C stemming from the left branch of the QTBT structure).Additional examples are shown in FIG. 6C where the larger child noderesulting from a 3:1 asymmetric partitioning is a restricted node and isnot further split before encoding and signaling.

After quadtree splitting and binary tree splitting using any of theparameters for a QTBT structure described above, the shapes representedby the QTBT’s final leaf nodes may represent the final CUs 102 to becoded, such as coding using inter prediction or intra prediction. Inaddition, the QTBT block structure may support the feature that luma andchroma have a separate QTBT structure. Currently, for P and B slices,the luma and chroma CTBs in one CTU share the same QTBT structure. For Islices, the luma CTB is partitioned into CUs by a QTBT structure, andthe chroma CTBs are partitioned into chroma CUs by another QTBTstructure. In one or more embodiments, a CU in an I slice may include acoding block of the luma component or coding blocks of two chromacomponents. In one or more embodiments, a CU in P and B slice a CUconsists of coding blocks of all three colour components. In one or moreembodiments, luma and chroma trees may be shared for an I slice.

In alternate embodiments JVET can use a two-level coding block structureas an alternative to, or extension of, the QTBT partitioning describedabove. In the two-level coding block structure, a CTU 100 can first bepartitioned at a high level into base units (BUs). The BUs can then bepartitioned at a low level into operating units (OUs).

In embodiments employing the two-level coding block structure, at thehigh level a CTU 100 can be partitioned into BUs according to one of theQTBT structures described above, or according to a quadtree (QT)structure such as the one used in HEVC in which blocks can only be splitinto four equally sized sub-blocks. By way of a non-limiting example, aCTU 102 can be partitioned into BUs according to the QTBT structuredescribed above with respect to FIGS. 5-6 , such that leaf nodes in thequadtree portion can be split using quadtree partitioning, symmetricbinary partitioning, or asymmetric binary partitioning. In this example,the final leaf nodes of the QTBT can be BUs instead of CUs.

At the lower level in the two-level coding block structure, each BUpartitioned from the CTU 100 can be further partitioned into one or moreOUs. In some embodiments, when the BU is square, it can be split intoOUs using quadtree partitioning or binary partitioning, such assymmetric or asymmetric binary partitioning. However, when the BU is notsquare, it can be split into OUs using binary partitioning only.Limiting the type of partitioning that can be used for non-square BUscan limit the number of bits used to signal the type of partitioningused to generate BUs.

Although the discussion below describes coding CUs 102, BUs and OUs canbe coded instead of CUs 102 in embodiments that use the two-level codingblock structure. By way of a non-limiting examples, BUs can be used forhigher level coding operations such as intra prediction or interprediction, while the smaller OUs can be used for lower level codingoperations such as transforms and generating transform coefficients.Accordingly, syntax for be coded for BUs that indicate whether they arecoded with intra prediction or inter prediction, or informationidentifying particular intra prediction modes or motion vectors used tocode the BUs. Similarly, syntax for OUs can identify particulartransform operations or quantized transform coefficients used to codethe OUs.

FIG. 7 depicts a simplified diagram for CU coding in a JVET encoder,which can produce a JVET compliant bitstream. The main stages of videocoding include partitioning to identify CUs 102 as described above,followed by encoding CUs 102 using prediction at 704 or 706, generationof a residual CU 710 at 708, transformation at 712, quantization at 716,and entropy coding at 720. The encoder and encoding process illustratedin FIG. 7 may also include processes that duplicate the decoding processemployed by a decoder, described in more detail below, such that theencoder will generate identical predictions for subsequent data. Thus,the final picture representation may be a duplicate of the output of thedecoder and stored in a reference buffer to be used for a prediction ofsubsequent picture.

Given a current CU 102, the encoder can obtain a prediction CU 702either spatially using intra prediction at 704 or temporally using interprediction at 706. The basic idea of prediction coding is to transmit adifferential, or residual, signal between the original signal and aprediction for the original signal. At the receiver side, the originalsignal can be reconstructed by adding the residual and the prediction,as will be described below. Because the differential signal has a lowercorrelation than the original signal, fewer bits are needed for itstransmission.

A sequence of coding units may make up a slice, and one or more slicesmay make up a picture. A slice may include one or more slice segments,each in its own NAL unit. A slice or slice segment may include headerinformation for the slice or bitstream. A slice is a data structure thatcan be decoded independently from other slices of the same picture, interms of entropy coding, signal prediction, and residual signalreconstruction. A slice can either be an entire picture or a region of apicture.

A slice, such as an entire picture or a portion of a picture, codedentirely with intra-predicted CUs 102 can be an I slice that can bedecoded without reference to other slices, and as such can be a possiblepoint where decoding can begin. A slice coded with at least someinter-predicted CUs can be a predictive (P) or bi-predictive (B) slicethat can be decoded based on one or more reference pictures. P slicesmay use intra-prediction and inter-prediction with previously codedslices. For example, P slices may be compressed further than theI-slices by the use of inter-prediction, but need the coding of apreviously coded slice to code them. B slices can use data from previousand/or subsequent slices for its coding, using intra-prediction orinter-prediction using an interpolated prediction from two differentframes, thus increasing the accuracy of the motion estimation process.In some cases P slices and B slices can also or alternately be encodedusing intra block copy, in which data from other portions of the sameslice is used.

As will be discussed below, intra prediction or inter prediction can beperformed based on reconstructed CUs 734 from previously coded CUs 102,such as neighboring CUs 102 or CUs 102 in reference pictures.

When a CU 102 is coded spatially with intra prediction at 704, an intraprediction mode can be found that best predicts pixel values of the CU102 based on samples from neighboring CUs 102 in the picture.

When coding a CU’s luma component, the encoder can generate a list ofcandidate intra prediction modes. While HEVC had 35 possible intraprediction modes for luma components, in JVET there are 67 possibleintra prediction modes for luma components. These include a planar modethat uses a three dimensional plane of values generated from neighboringpixels, a DC mode that uses values averaged from neighboring pixels, andthe 65 directional modes shown in FIG. 8 that use values copied fromneighboring pixels along the indicated directions.

When generating a list of candidate intra prediction modes for a CU’sluma component, the number of candidate modes on the list can depend onthe CU’s size. The candidate list can include: a subset of HEVC’s 35modes with the lowest SATD (Sum of Absolute Transform Difference) costs;new directional modes added for JVET that neighbor the candidates foundfrom the HEVC modes; and modes from a set of six most probable modes(MPMs) for the CU 102 that are identified based on intra predictionmodes used for previously coded neighboring blocks as well as a list ofdefault modes.

When coding a CU’s chroma components, a list of candidate intraprediction modes can also be generated. The list of candidate modes caninclude modes generated with cross-component linear model projectionfrom luma samples, intra prediction modes found for luma CBs inparticular collocated positions in the chroma block, and chromaprediction modes previously found for neighboring blocks. The encodercan find the candidate modes on the lists with the lowest ratedistortion costs, and use those intra prediction modes when coding theCU’s luma and chroma components. For example, an encoderrater-distortion optimization process of the QTBT structure may be usedto determine the best block partitioning shape. Syntax can be coded inthe bitstream that indicates the intra prediction modes used to codeeach CU 102.

After the best intra prediction modes for a CU 102 have been selected,the encoder can generate a prediction CU 402 using those modes. When theselected modes are directional modes, a 4-tap filter can be used toimprove the directional accuracy. Columns or rows at the top or leftside of the prediction block can be adjusted with boundary predictionfilters, such as 2-tap or 3-tap filters.

The prediction CU 702 can be smoothed further with a position dependentintra prediction combination (PDPC) process that adjusts a prediction CU702 generated based on filtered samples of neighboring blocks usingunfiltered samples of neighboring blocks, or adaptive reference samplesmoothing using 3-tap or 5-tap low pass filters to process referencesamples.

When a CU 102 is coded temporally with inter prediction at 706, a set ofmotion vectors (MVs) can be found that points to samples in referencepictures that best predict pixel values of the CU 102. Inter predictionexploits temporal redundancy between slices by representing adisplacement of a block of pixels in a slice. The displacement isdetermined according to the value of pixels in previous or followingslices through a process called motion compensation. Motion vectors andassociated reference indices that indicate pixel displacement relativeto a particular reference picture can be provided in the bitstream to adecoder, along with the residual between the original pixels and themotion compensated pixels. The decoder can use the residual and signaledmotion vectors and reference indices to reconstruct a block of pixels ina reconstructed slice.

In JVET, motion vector accuracy can be stored at 1/16 pel, and thedifference between a motion vector and a CU’s predicted motion vectorcan be coded with either quarter-pel resolution or integer-pelresolution.

In JVET motion vectors can be found for multiple sub-CUs within a CU102, using techniques such as advanced temporal motion vector prediction(ATMVP), spatial-temporal motion vector prediction (STMVP), affinemotion compensation prediction, pattern matched motion vector derivation(PMMVD), and/or bi-directional optical flow (BIO).

Using ATMVP, the encoder can find a temporal vector for the CU 102 thatpoints to a corresponding block in a reference picture. The temporalvector can be found based on motion vectors and reference pictures foundfor previously coded neighboring CUs 102. Using the reference blockpointed to by a temporal vector for the entire CU 102, a motion vectorcan be found for each sub-CU within the CU 102.

STMVP can find motion vectors for sub-CUs by scaling and averagingmotion vectors found for neighboring blocks previously coded with interprediction, together with a temporal vector.

Affine motion compensation prediction can be used to predict a field ofmotion vectors for each sub-CU in a block, based on two control motionvectors found for the top corners of the block. For example, motionvectors for sub-CUs can be derived based on top corner motion vectorsfound for each 4×4 block within the CU 102.

PMMVD can find an initial motion vector for the current CU 102 usingbilateral matching or template matching. Bilateral matching can look atthe current CU 102 and reference blocks in two different referencepictures along a motion trajectory, while template matching can look atcorresponding blocks in the current CU 102 and a reference pictureidentified by a template. The initial motion vector found for the CU 102can then be refined individually for each sub-CU.

BIO can be used when inter prediction is performed with bi-predictionbased on earlier and later reference pictures, and allows motion vectorsto be found for sub-CUs based on the gradient of the difference betweenthe two reference pictures.

In some situations local illumination compensation (LIC) can be used atthe CU level to find values for a scaling factor parameter and an offsetparameter, based on samples neighboring the current CU 102 andcorresponding samples neighboring a reference block identified by acandidate motion vector. In JVET, the LIC parameters can change and besignaled at the CU level.

For some of the above methods the motion vectors found for each of aCU’s sub-CUs can be signaled to decoders at the CU level. For othermethods, such as PMMVD and BIO, motion information is not signaled inthe bitstream to save overhead, and decoders can derive the motionvectors through the same processes.

After the motion vectors for a CU 102 have been found, the encoder cangenerate a prediction CU 702 using those motion vectors. In some cases,when motion vectors have been found for individual sub-CUs, OverlappedBlock Motion Compensation (OBMC) can be used when generating aprediction CU 702 by combining those motion vectors with motion vectorspreviously found for one or more neighboring sub-CUs.

When bi-prediction is used, JVET can use decoder-side motion vectorrefinement (DMVR) to find motion vectors. DMVR allows a motion vector tobe found based on two motion vectors found for bi-prediction using abilateral template matching process. In DMVR, a weighted combination ofprediction CUs 702 generated with each of the two motion vectors can befound, and the two motion vectors can be refined by replacing them withnew motion vectors that best point to the combined prediction CU 702.The two refined motion vectors can be used to generate the finalprediction CU 702.

At 708, once a prediction CU 702 has been found with intra prediction at704 or inter prediction at 706 as described above, the encoder cansubtract the prediction CU 702 from the current CU 102 find a residualCU 710.

The encoder can use one or more transform operations at 712 to convertthe residual CU 710 into transform coefficients 714 that express theresidual CU 710 in a transform domain, such as using a discrete cosineblock transform (DCT-transform) to convert data into the transformdomain. JVET allows more types of transform operations than HEVC,including DCT-II, DST-VII, DST-VII, DCT-VIII, DST-I, and DCT-Voperations. The allowed transform operations can be grouped intosub-sets, and an indication of which sub-sets and which specificoperations in those sub-sets were used can be signaled by the encoder.In some cases, large block-size transforms can be used to zero out highfrequency transform coefficients in CUs 102 larger than a certain size,such that only lower-frequency transform coefficients are maintained forthose CUs 102.

In some cases a mode dependent non-separable secondary transform(MDNSST) can be applied to low frequency transform coefficients 714after a forward core transform. The MDNSST operation can use aHypercube-Givens Transform (HyGT) based on rotation data. When used, anindex value identifying a particular MDNSST operation can be signaled bythe encoder.

At 716, the encoder can quantize the transform coefficients 714 intoquantized transform coefficients 716. The quantization of eachcoefficient may be computed by dividing a value of the coefficient by aquantization step, which is derived from a quantization parameter (QP).In some embodiments, the Qstep is defined as 2^((QP-4)/6). Because highprecision transform coefficients 714 can be converted into quantizedtransform coefficients 716 with a finite number of possible values,quantization can assist with data compression. Thus, quantization of thetransform coefficients may limit an amount of bits generated and sent bythe transformation process. However, while quantization is a lossyoperation, and the loss by quantization cannot be recovered, thequantization process presents a trade-off between quality of thereconstructed sequence and an amount of information needed to representthe sequence. For example, a lower QP value can result in better qualitydecoded video, although a higher amount of data may be required forrepresentation and transmission. In contrast, a high QP value can resultin lower quality reconstructed video sequences but with lower data andbandwidth needs.

JVET can utilize variance-based adaptive quantization techniques, whichallows every CU 102 to use a different quantization parameter for itscoding process (instead of using the same frame QP in the coding ofevery CU 102 of the frame). The variance-based adaptive quantizationtechniques adaptively lowers the quantization parameter of certainblocks while increasing it in others. To select a specific QP for a CU102, the CU’s variance is computed. In brief, if a CU’s variance ishigher than the average variance of the frame, a higher QP than theframe’s QP may be set for the CU 102. If the CU 102 presents a lowervariance than the average variance of the frame, a lower QP may beassigned.

At 720, the encoder can find final compression bits 722 by entropycoding the quantized transform coefficients 718. Entropy coding aims toremove statistical redundancies of the information to be transmitted. InJVET, CABAC (Context Adaptive Binary Arithmetic Coding) can be used tocode the quantized transform coefficients 718, which uses probabilitymeasures to remove the statistical redundancies. For CUs 102 withnon-zero quantized transform coefficients 718, the quantized transformcoefficients 718 can be converted into binary. Each bit (“bin”) of thebinary representation can then be encoded using a context model. A CU102 can be broken up into three regions, each with its own set ofcontext models to use for pixels within that region.

Multiple scan passes can be performed to encode the bins. During passesto encode the first three bins (bin0, bin1, and bin2), an index valuethat indicates which context model to use for the bin can be found byfinding the sum of that bin position in up to five previously codedneighboring quantized transform coefficients 718 identified by atemplate.

A context model can be based on probabilities of a bin’s value being ‘0’or ‘1’. As values are coded, the probabilities in the context model canbe updated based on the actual number of ‘0’ and ‘1’ values encountered.While HEVC used fixed tables to re-initialize context models for eachnew picture, in JVET the probabilities of context models for newinter-predicted pictures can be initialized based on context modelsdeveloped for previously coded inter-predicted pictures.

The encoder can produce a bitstream that contains entropy encoded bits722 of residual CUs 710, prediction information such as selected intraprediction modes or motion vectors, indicators of how the CUs 102 werepartitioned from a CTU 100 according to the QTBT structure, and/or otherinformation about the encoded video. The bitstream can be decoded by adecoder as discussed below.

In addition to using the quantized transform coefficients 718 to findthe final compression bits 722, the encoder can also use the quantizedtransform coefficients 718 to generate reconstructed CUs 734 byfollowing the same decoding process that a decoder would use to generatereconstructed CUs 734. Thus, once the transformation coefficients havebeen computed and quantized by the encoder, the quantized transformcoefficients 718 may be transmitted to the decoding loop in the encoder.After quantization of a CU’s transform coefficients, a decoding loopallows the encoder to generate a reconstructed CU 734 identical to theone the decoder generates in the decoding process. Accordingly, theencoder can use the same reconstructed CUs 734 that a decoder would usefor neighboring CUs 102 or reference pictures when performing intraprediction or inter prediction for a new CU 102. Reconstructed CUs 102,reconstructed slices, or full reconstructed frames may serve asreferences for further prediction stages.

At the encoder’s decoding loop (and see below, for the same operationsin the decoder) to obtain pixel values for the reconstructed image, adequantization process may be performed. To dequantize a frame, forexample, a quantized value for each pixel of a frame is multiplied bythe quantization step, e.g., (Qstep) described above, to obtainreconstructed dequantized transform coefficients 726. For example, inthe decoding process shown in FIG. 7 in the encoder, the quantizedtransform coefficients 718 of a residual CU 710 can be dequantized at724 to find dequantized transform coefficients 726. If an MDNSSToperation was performed during encoding, that operation can be reversedafter dequantization.

At 728, the dequantized transform coefficients 726 can be inversetransformed to find a reconstructed residual CU 730, such as by applyinga DCT to the values to obtain the reconstructed image. At 732 thereconstructed residual CU 730 can be added to a corresponding predictionCU 702 found with intra prediction at 704 or inter prediction at 706, inorder to find a reconstructed CU 734. While in some embodiments theencoder can perform intra prediction at 704 as described above, in otherembodiments the encoder can follow the process disclosed herein forintra prediction template matching to generate a prediction CU 702 inthe same way that a decoder would use template matching for intraprediction if information identifying the intra prediction mode used forthe CU 102 is omitted from the bitstream.

At 736, one or more filters can be applied to the reconstructed dataduring the decoding process (in the encoder or, as described below, inthe decoder), at either a picture level or CU level. For example, theencoder can apply a deblocking filter, a sample adaptive offset (SAO)filter, and/or an adaptive loop filter (ALF). The encoder’s decodingprocess may implement filters to estimate and transmit to a decoder theoptimal filter parameters that can address potential artifacts in thereconstructed image. Such improvements increase the objective andsubjective quality of the reconstructed video. In deblocking filtering,pixels near a sub-CU boundary may be modified, whereas in SAO, pixels ina CTU 100 may be modified using either an edge offset or band offsetclassification. JVET’s ALF can use filters with circularly symmetricshapes for each 2×2 block. An indication of the size and identity of thefilter used for each 2×2 block can be signaled.

If reconstructed pictures are reference pictures, they can be stored ina reference buffer 738 for inter prediction of future CUs 102 at 706.

During the above steps, JVET allows a content adaptive clippingoperations to be used to adjust color values to fit between lower andupper clipping bounds. The clipping bounds can change for each slice,and parameters identifying the bounds can be signaled in the bitstream.

FIG. 9 depicts a simplified block diagram for CU coding in a JVETdecoder. A decoder is an embodiment of a decoding process, which is aprocess specified for JVET that reads a bitstream and derives decodedpictures from it. A process in this context describes the decoding ofsyntax elements. A bitstream conforming to JVET may include slicesegment data for each coding tree unit of a coded picture, such that thedivision of the pictures into slices or slice segments and then intocoding tree units may form the partitioning of the picture. The codedpicture may be a coded representation of a picture. In one or moreembodiments, the coded picture may comprise VCL NAL units with aparticular value within an access unit, and may include all of thecoding tree units in the picture.

As described above, FIG. 3 is one example of a coding treerepresentation that is provided via syntax elements in the bitstream tothe decoder, where the decoder can recreate the partition of the codingtree unit based on each child node,, and parent coding unit representedby the syntax in the bitstream. Thus, the decoding process may beinvoked when parsing slice segment data syntax or coding tree unitsyntax.

A JVET decoder can receive a bitstream containing information aboutencoded CUs 102. The bitstream can indicate how CUs 102 of a picturewere partitioned from a CTU 100 according to a QTBT structure. By way ofa non-limiting example, the bitstream can identify how CUs 102 werepartitioned from each CTU 100 in a QTBT using quadtree partitioning,symmetric binary partitioning, and/or asymmetric binary partitioning.The bitstream can also indicate prediction information for the CUs 102such as intra prediction modes or motion vectors, and bits 902representing entropy encoded residual CUs. In some embodiments theencoder can have omitted information in the bitstream about intraprediction modes used to encode some or all CUs 102 coded using intraprediction, and as such the decoder can use template matching for intraprediction as described below with respect to the following figures.

At 904 the decoder can decode the entropy encoded bits 902 using theCABAC context models signaled in the bitstream by the encoder. Thedecoder can use parameters signaled by the encoder to update the contextmodels’ probabilities in the same way they were updated during encoding.

After reversing the entropy encoding at 904 to find quantized transformcoefficients 906, the decoder can dequantize them at 908 to finddequantized transform coefficients 910. If an MDNSST operation wasperformed during encoding, that operation can be reversed by the decoderafter dequantization.

At 912, the dequantized transform coefficients 910 can be inversetransformed to find a reconstructed residual CU 914. At 916, thereconstructed residual CU 914 can be added to a corresponding predictionCU 926 found with intra prediction at 922 or inter prediction at 924, inorder to find a reconstructed CU 918.

At 920, one or more filters can be applied to the reconstructed data, ateither a picture level or CU level. For example, the decoder can apply adeblocking filter, a sample adaptive offset (SAO) filter, and/or anadaptive loop filter (ALF). As described above, the in-loop filterslocated in the decoding loop of the encoder may be used to estimateoptimal filter parameters to increase the objective and subjectivequality of a frame. These parameters are transmitted to the decoder tofilter the reconstructed frame at 920 to match the filteredreconstructed frame in the encoder.

After reconstructed pictures have been generated by findingreconstructed CUs 918 and applying signaled filters, the decoder canoutput the reconstructed pictures as output video 928. If reconstructedpictures are to be used as reference pictures, they can be stored in areference buffer 930 for inter prediction of future CUs 102 at 924.

FIG. 10 depicts an embodiment of a method of CU coding 1000 in a JVETdecoder. In the embodiment depicted in FIG. 10 , in step 1002 an encodedbitstream 902 can be received and then in step 1004 the CABAC contextmodel associated with the encoded bitstream 902 can be determined andthe encoded bitstream 902 can then be decoded using the determined CABACcontext model in step 1006.

In step 1008, the quantized transform coefficients 906 associated withthe encoded bitstream 902 can be determined and de-quantized transformcoefficients 910 can then be determined from the quantized transformcoefficients 906 in step 1010.

In step 1012, it can be determined whether an MDNSST operation wasperformed during encoding and/or if the bitstream 902 containsindications that an MDNSST operation was applied to the bitstream 902.If it is determined that an MDNSST operation was performed during theencoding process or the bitstream 902 contains indications that anMDNSST operation was applied to the bitstream 902, then an inverseMDNSST operation 1014 can be implemented before an inverse transformoperation 912 is performed on the bitstream 902 in step 1016.Alternately, an inverse transform operation 912 can be performed on thebitstream 902 in step 1016 absent application of an inverse MDNSSToperation in step 1014. The inverse transform operation 912 in step 1016can determine and/or construct a reconstructed residual CU 914.

In step 1018, the reconstructed residual CU 914 from step 1016 can becombined with a prediction CU 918. The prediction CU 918 can be one ofan intra-prediction CU 922 determined in step 1020 and aninter-prediction unit 924 determined in step 1022.

In step 1024, any one or more filters 920 can be applied to thereconstructed CU 914 and output in step 1026. In some embodimentsfilters 920 may not be applied in step 1024.

In some embodiments, in step 1028, the reconstructed CU 918 can bestored in a reference buffer 930.

The execution of the sequences of instructions required to practice theembodiments can be performed by a computer system 1100 as shown in FIG.11 . In an embodiment, execution of the sequences of instructions isperformed by a single computer system 1100. According to otherembodiments, two or more computer systems 1100 coupled by acommunication link 1115 can perform the sequence of instructions incoordination with one another. Although a description of only onecomputer system 1100 will be presented below, however, it should beunderstood that any number of computer systems 1100 can be employed topractice the embodiments.

A computer system 1100 according to an embodiment will now be describedwith reference to FIG. 11 , which is a block diagram of the functionalcomponents of a computer system 1100. As used herein, the term computersystem 1100 is broadly used to describe any computing device that canstore and independently run one or more programs.

Each computer system 1100 can include a communication interface 1114coupled to the bus 1106. The communication interface 1114 providestwo-way communication between computer systems 1100. The communicationinterface 1114 of a respective computer system 1100 transmits andreceives electrical, electromagnetic or optical signals, which includedata streams representing various types of signal information, e.g.,instructions, messages and data. A communication link 1115 links onecomputer system 1100 with another computer system 1100. For example, thecommunication link 1115 can be a LAN, in which case the communicationinterface 1114 can be a LAN card, or the communication link 1115 can bea PSTN, in which case the communication interface 1114 can be anintegrated services digital network (ISDN) card or a modem, or thecommunication link 1115 can be the Internet, in which case thecommunication interface 1114 can be a dial-up, cable or wireless modem.

A computer system 1100 can transmit and receive messages, data, andinstructions, including program, i.e., application, code, through itsrespective communication link 1115 and communication interface 1114.Received program code can be executed by the respective processor(s)1107 as it is received, and/or stored in the storage device 1110, orother associated non-volatile media, for later execution.

In an embodiment, the computer system 1100 operates in conjunction witha data storage system 1131, e.g., a data storage system 1131 thatcontains a database 1132 that is readily accessible by the computersystem 1100. The computer system 1100 communicates with the data storagesystem 1131 through a data interface 1133. A data interface 1133, whichis coupled to the bus 1106, transmits and receives electrical,electromagnetic or optical signals, which include data streamsrepresenting various types of signal information, e.g., instructions,messages and data. In embodiments, the functions of the data interface1133 can be performed by the communication interface 1114.

Computer system 1100 includes a bus 1106 or other communicationmechanism for communicating instructions, messages and data,collectively, information, and one or more processors 1107 coupled withthe bus 1106 for processing information. Computer system 1100 alsoincludes a main memory 1108, such as a random access memory (RAM) orother dynamic storage device, coupled to the bus 1106 for storingdynamic data and instructions to be executed by the processor(s) 1107.The main memory 1108 also can be used for storing temporary data, i.e.,variables, or other intermediate information during execution ofinstructions by the processor(s) 1107.

The computer system 1100 can further include a read only memory (ROM)1109 or other static storage device coupled to the bus 1106 for storingstatic data and instructions for the processor(s) 1107. A storage device1110, such as a magnetic disk or optical disk, can also be provided andcoupled to the bus 1106 for storing data and instructions for theprocessor(s) 1107.

A computer system 1100 can be coupled via the bus 1106 to a displaydevice 1111, such as, but not limited to, a cathode ray tube (CRT) or aliquid-crystal display (LCD) monitor, for displaying information to auser. An input device 1112, e.g., alphanumeric and other keys, iscoupled to the bus 1106 for communicating information and commandselections to the processor(s) 1107.

According to one embodiment, an individual computer system 1100 performsspecific operations by their respective processor(s) 1107 executing oneor more sequences of one or more instructions contained in the mainmemory 1108. Such instructions can be read into the main memory 1108from another computer-usable medium, such as the ROM 1109 or the storagedevice 1110. Execution of the sequences of instructions contained in themain memory 1108 causes the processor(s) 1107 to perform the processesdescribed herein. In alternative embodiments, hard-wired circuitry canbe used in place of or in combination with software instructions. Thus,embodiments are not limited to any specific combination of hardwarecircuitry and/or software.

The term “computer-usable medium,” as used herein, refers to any mediumthat provides information or is usable by the processor(s) 1107. Such amedium can take many forms, including, but not limited to, non-volatile,volatile and transmission media. Non-volatile media, i.e., media thatcan retain information in the absence of power, includes the ROM 1109,CD ROM, magnetic tape, and magnetic discs. Volatile media, i.e., mediathat cannot retain information in the absence of power, includes themain memory 1108. Transmission media includes coaxial cables, copperwire and fiber optics, including the wires that comprise the bus 1106.Transmission media can also take the form of carrier waves; i.e.,electromagnetic waves that can be modulated, as in frequency, amplitudeor phase, to transmit information signals. Additionally, transmissionmedia can take the form of acoustic or light waves, such as thosegenerated during radio wave and infrared data communications. In theforegoing specification, the embodiments have been described withreference to specific elements thereof. It will, however, be evidentthat various modifications and changes can be made thereto withoutdeparting from the broader spirit and scope of the embodiments. Forexample, the reader is to understand that the specific ordering andcombination of process actions shown in the process flow diagramsdescribed herein is merely illustrative, and that using different oradditional process actions, or a different combination or ordering ofprocess actions can be used to enact the embodiments. The specificationand drawings are, accordingly, to be regarded in an illustrative ratherthan restrictive sense

It should also be noted that the present invention can be implemented ina variety of computer systems. The various techniques described hereincan be implemented in hardware or software, or a combination of both.Preferably, the techniques are implemented in computer programsexecuting on programmable computers that each include a processor, astorage medium readable by the processor (including volatile andnon-volatile memory and/or storage elements), at least one input device,and at least one output device. Program code is applied to data enteredusing the input device to perform the functions described above and togenerate output information. The output information is applied to one ormore output devices. Each program is preferably implemented in a highlevel procedural or object oriented programming language to communicatewith a computer system. However, the programs can be implemented inassembly or machine language, if desired. In any case, the language canbe a compiled or interpreted language. Each such computer program ispreferably stored on a storage medium or device (e.g., ROM or magneticdisk) that is readable by a general or special purpose programmablecomputer for configuring and operating the computer when the storagemedium or device is read by the computer to perform the proceduresdescribed above. The system can also be considered to be implemented asa computer-readable storage medium, configured with a computer program,where the storage medium so configured causes a computer to operate in aspecific and predefined manner. Further, the storage elements of theexemplary computing applications can be relational or sequential (flatfile) type computing databases that are capable of storing data invarious combinations and configurations.

FIG. 12 is a flow diagram that illustrates a method for performing thedisclosed techniques, but it should be understood that the techniquesdescribed herein with respect to the remaining figures similarly capturethe methods available using the disclosed techniques. As illustrated inFIG. 12 , a JVET encoder or decoder, such as those described in FIGS. 7,9, and 13 , may receive a bitstream at 1202 indicating how a coding treeunit was partitioned in to coding units, such as a bitstream with asyntax structure such as that shown in FIG. 6C. At 1204, the encoder ordecoder may parse the bitstream to determine each of a partitioningmethod (e.g., binary, quadtree), a partitioning type (e.g., a verticalor horizontal split in which type shown in FIG. 5 , for example). At1206, the encoder or decoder can identify each of the child nodes withineach respective parent unit to form a tree structure representation. At1208, the encoder may encode the coding units according to the treestructure to provide to a decoder, or the encoder may provide theencoding coding units to an internal decoding process as described withrespect to FIG. 7 . At 1208, a decoder may decode the identified codingunits according to the tree structure using JVET processes.

FIG. 13 is a high level view of a source device 12 and destinationdevice 10 that may incorporate features of the systems and devicesdescribed herein. As shown in FIG. 13 , example video coding system 10includes a source device 12 and a destination device 14 where, in thisexample, the source device 12 generates encoded video data. Accordingly,source device 12 may be referred to as a video encoding device.Destination device 14 may decode the encoded video data generated bysource device 12. Accordingly, destination device 14 may be referred toas a video decoding device. Source device 12 and destination device 14may be examples of video coding devices.

Destination device 14 may receive encoded video data from source device12 via a channel 16. Channel 16 may comprise a type of medium or devicecapable of moving the encoded video data from source device 12 todestination device 14. In one example, channel 16 may comprise acommunication medium that enables source device 12 to transmit encodedvideo data directly to destination device 14 in real-time.

In this example, source device 12 may modulate the encoded video dataaccording to a communication standard, such as a wireless communicationprotocol, and may transmit the modulated video data to destinationdevice 14. The communication medium may comprise a wireless or wiredcommunication medium, such as a radio frequency (RF) spectrum or one ormore physical transmission lines. The communication medium may form partof a packet-based network, such as a local area network, a wide-areanetwork, or a global network such as the Internet. The communicationmedium may include routers, switches, base stations, or other equipmentthat facilitates communication from source device 12 to destinationdevice 14. In another example, channel 16 may correspond to a storagemedium that stores the encoded video data generated by source device 12.

In the example of FIG. 13 , source device 12 includes a video source 18,video encoder 20, and an output interface 22. In some cases, outputinterface 28 may include a modulator/demodulator (modem) and/or atransmitter. In source device 12, video source 18 may include a sourcesuch as a video capture device, e.g., a video camera, a video archivecontaining previously captured video data, a video feed interface toreceive video data from a video content provider, and/or a computergraphics system for generating video data, or a combination of suchsources.

Video encoder 20 may encode the captured, pre-captured, orcomputer-generated video data. An input image may be received by thevideo encoder 20 and stored in the input frame memory 21. The generalpurpose processor 23 may load information from here and performencoding. The program for driving the general purpose processor may beloaded from a storage device, such as the example memory modulesdepicted in FIG. 13 . The general purpose processor may use processingmemory 22 to perform the encoding, and the output of the encodinginformation by the general processor may be stored in a buffer, such asoutput buffer 26.

The video encoder 20 may include a resampling module 25 which may beconfigured to code (e.g., encode) video data in a scalable video codingscheme that defines at least one base layer and at least one enhancementlayer. Resampling module 25 may resample at least some video data aspart of an encoding process, wherein resampling may be performed in anadaptive manner using resampling filters.

The encoded video data, e.g., a coded bit stream, may be transmitteddirectly to destination device 14 via output interface 28 of sourcedevice 12. In the example of FIG. 13 , destination device 14 includes aninput interface 38, a video decoder 30, and a display device 32. In somecases, input interface 28 may include a receiver and/or a modem. Inputinterface 38 of destination device 14 receives encoded video data overchannel 16. The encoded video data may include a variety of syntaxelements generated by video encoder 20 that represent the video data.Such syntax elements may be included with the encoded video datatransmitted on a communication medium, stored on a storage medium, orstored a file server.

The encoded video data may also be stored onto a storage medium or afile server for later access by destination device 14 for decodingand/or playback. For example, the coded bitstream may be temporarilystored in the input buffer 31, then loaded in to the general purposeprocessor 33. The program for driving the general purpose processor maybe loaded from a storage device or memory. The general purpose processormay use a process memory 32 to perform the decoding. The video decoder30 may also include a resampling module 35 similar to the resamplingmodule 25 employed in the video encoder 20.

FIG. 13 depicts the resampling module 35 separately from the generalpurpose processor 33, but it would be appreciated by one of skill in theart that the resampling function may be performed by a program executedby the general purpose processor, and the processing in the videoencoder may be accomplished using one or more processors. The decodedimage(s) may be stored in the output frame buffer 36 and then sent outto the input interface 38.

Display device 38 may be integrated with or may be external todestination device 14. In some examples, destination device 14 mayinclude an integrated display device and may also be configured tointerface with an external display device. In other examples,destination device 14 may be a display device. In general, displaydevice 38 displays the decoded video data to a user.

Video encoder 20 and video decoder 30 may operate according to a videocompression standard. ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC29/WG 11) are studying the potential need for standardization of futurevideo coding technology with a compression capability that significantlyexceeds that of the current High Efficiency Video Coding HEVC standard(including its current extensions and near-term extensions for screencontent coding and high-dynamic-range coding). The groups are workingtogether on this exploration activity in a joint collaboration effortknown as the Joint Video Exploration Team (JVET) to evaluate compressiontechnology designs proposed by their experts in this area. A recentcapture of JVET development is described in the “Algorithm Descriptionof Joint Exploration Test Model 5 (JEM 5)”, JVET-E1001-V2, authored byJ. Chen, E. Alshina, G. Sullivan, J. Ohm, J. Boyce.

Additionally or alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards thatfunction with the disclosed JVET features. Thus, other standards such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thus,while newly developed for JVET, techniques of this disclosure are notlimited to any particular coding standard or technique. Other examplesof video compression standards and techniques include MPEG-2, ITU-TH.263 and proprietary or open source compression formats and relatedformats.

Video encoder 20 and video decoder 30 may be implemented in hardware,software, firmware or any combination thereof. For example, the videoencoder 20 and decoder 30 may employ one or more processors, digitalsignal processors (DSPs), application specific integrated circuits(ASICs), field programmable gate arrays (FPGAs), discrete logic, or anycombinations thereof. When the video encoder 20 and decoder 30 areimplemented partially in software, a device may store instructions forthe software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Each of videoencoder 20 and video decoder 30 may be included in one or more encodersor decoders, either of which may be integrated as part of a combinedencoder/decoder (CODEC) in a respective device.

Aspects of the subject matter described herein may be described in thegeneral context of computer-executable instructions, such as programmodules, being executed by a computer, such as the general purposeprocessors 23 and 33 described above. Generally, program modules includeroutines, programs, objects, components, data structures, and so forth,which perform particular tasks or implement particular abstract datatypes. Aspects of the subject matter described herein may also bepracticed in distributed computing environments where tasks areperformed by remote processing devices that are linked through acommunications network. In a distributed computing environment, programmodules may be located in both local and remote computer storage mediaincluding memory storage devices.

Examples of memory include random access memory (RAM), read only memory(ROM), or both. Memory may store instructions, such as source code orbinary code, for performing the techniques described above. Memory mayalso be used for storing variables or other intermediate informationduring execution of instructions to be executed by a processor, such asprocessor 23 and 33.

A storage device may also store instructions, instructions, such assource code or binary code, for performing the techniques describedabove. A storage device may additionally store data used and manipulatedby the computer processor. For example, a storage device in a videoencoder 20 or a video decoder 30 may be a database that is accessed bycomputer system 23 or 33. Other examples of storage device includerandom access memory (RAM), read only memory (ROM), a hard drive, amagnetic disk, an optical disk, a CD-ROM, a DVD, a flash memory, a USBmemory card, or any other medium from which a computer can read.

A memory or storage device may be an example of a non-transitorycomputer-readable storage medium for use by or in connection with thevideo encoder and/or decoder. The non-transitory computer-readablestorage medium contains instructions for controlling a computer systemto be configured to perform functions described by particularembodiments. The instructions, when executed by one or more computerprocessors, may be configured to perform that which is described inparticular embodiments.

Also, it is noted that some embodiments have been described as a processwhich can be depicted as a flow diagram or block diagram. Although eachmay describe the operations as a sequential process, many of theoperations can be performed in parallel or concurrently. In addition,the order of the operations may be rearranged. A process may haveadditional steps not included in the figures.

Particular embodiments may be implemented in a non-transitorycomputer-readable storage medium for use by or in connection with theinstruction execution system, apparatus, system, or machine. Thecomputer-readable storage medium contains instructions for controlling acomputer system to perform a method described by particular embodiments.The computer system may include one or more computing devices. Theinstructions, when executed by one or more computer processors, may beconfigured to perform that which is described in particular embodiments

As used in the description herein and throughout the claims that follow,“a”, “an”, and “the” includes plural references unless the contextclearly dictates otherwise. Also, as used in the description herein andthroughout the claims that follow, the meaning of “in” includes “in” and“on” unless the context clearly dictates otherwise.

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.

Although embodiments have been disclosed herein in detail and inlanguage specific to structural features and/or methodological actsabove, it is to be understood that those skilled in the art will readilyappreciate that many additional modifications are possible in theexemplary embodiments without materially departing from the novelteachings and advantages of the invention. Moreover, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Accordingly, these and all such modifications are intended to beincluded within the scope of this invention construed in breadth andscope in accordance with the appended claims.

1-20. (canceled)
 21. A method of decoding a bitstream, the methodcomprising: receiving a bitstream indicating how a coding tree unit waspartitioned into coding units according to a partitioning structure thatallows nodes to be split with at least one of quaternary treepartitioning, symmetric binary tree partitioning, and/or asymmetric treepartitioning; parsing said bitstream to determine if at least one ofasymmetric tree partitioning and/or symmetric binary tree partitioningsplits a parent node into child nodes, wherein symmetric binary treepartitioning splits a parent node into a plurality of child nodes ofequal size each of which are rectangular in shape, and asymmetric treepartitioning splits a parent node into a plurality of child nodes ofunequal size each of which are rectangular in shape; identifying each ofthe child nodes within each respective parent unit, wherein a node canbe recursively partitioned into smaller nodes; wherein the partitioningstructure allows both asymmetric tree partitioning and symmetric binarytree partitioning to occur in either order during recursivepartitioning; wherein the partitioning structure allows furtherpartitioning of child nodes that are produced from asymmetric treepartitioning of at least one parent node; and decoding the identifiedcoding units using an intra decoding process.
 22. The method of claim21, wherein said asymmetric tree partitioning produces child nodeshaving a size ratio that is anything other than
 1. 23. The method ofclaim 22, wherein at least one node is asymmetrically partitionedincluding two child nodes of unequal sizes, where a larger child node isthree times as large as a smaller child node for a size ratio of 3:1.24. The method of claim 22, wherein at least one node is asymmetricallypartitioned including two child nodes of unequal sizes, where a largerchild node is two times as large as a smaller child node for a sizeratio of 2:1.